Sensor RGB Filter
Each colored square of this pattern represents one pixel in the camera's image sensor. Here you see an array of 32x32 pixels expanded to easily view individual pixel elements; a very small area of the original 3888x2592 pixel array.
The camera image sensor's next layer is the Bayer Filter; a checkerboard pattern of Red, Green and Blue optical filters. There is one color square aligned with each sensor element in pattern groups of 4 pixels. Two elements are Green and the other two are Red and Blue. This means two things: 1) half of the pixel elements are detecting Green and 2) it takes 4 pixels to detect RGB color!
There are many more rod cells in the eye (which detect intensity but not color) than cone cells (which detect color). This RGB filter pattern, named after Bryce Bayer of the Eastman Kodak Company, was designed to mimic this sensitivity pattern of the human eye.
This RGB pattern is not a photo of the actual Bayer filter, but is a computer generated pattern of the same characteristics provided by a Bayer filter.